Determining an earth formation porosity from a detector response that is independent of the density of the formation

摘要

A neutron measurement method for determining the porosity of an earth formation surrounding a borehole 7; the method comprises the steps of: conveying a tool 4 along the borehole 7 in which the tool has a source S of neutron radiation and at least one detector N, F; generating measured response of the detector N, F that indicates the neutron interaction with the earth formation; operating the measured response with a predetermined mathematical equation and obtaining a corrected response that is independent of the density of the earth formation, and finally determining the porosity of the earth formation surrounding the borehole from the corrected response. The detector response may include responses from far 3 and near 2 detectors. The mathematical equation may be in the form of EMI ID=2.1 HE=7 WI=33 LX=247 LY=1246 TI=MF PCwhere CR= corrected detector rate; CR =measured detector rate; b = detector sensitivity to density; p =formation density. The source may be an isotopic neutron source, and the detectors may be thermal or epithermal detectors.